Patients co-infected with human immunodeficiency virus (HIV) and hepatitis B virus (HBV) who have advanced liver disease (decompensated cirrhosis by Child-Pugh score and no known cause of hepatitis other than HBV), a HBV viral load of at least 1 million copies/mL blood, and at least one year of therapy with lamivudine will be treated with open-label adefovir dipivoxil 10 mg daily and lamivudine 150 mg bid to evaluate the safety and efficacy of this regimen in this patient group and to obtain specimens for studies of immune responses to HBV in HIV-infected patients. Additionally the kinetics of viral load response to adefovir will be assessed. Specimens will be stored for possible use in evaluating HBV and HIV resistance to adefovir. L-carnitine supplementation will be used only if low serum carnitine levels are documented. Patients will be followed for HBV viral load response to adefovir for 48 weeks with possible extension. The primary study endpoints will be HBV viral load at week 24 (per-protocol patients) and DAVG at week 24 (intent-to-treat patients). Adefovir will be discontinued for toxicity; there will be no dose reduction. Up to 30 subjects will be enrolled.